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Abstract
We evaluated the performance of various detectors for small-field dosimetry with field sizes defined by a high-definition (HD) multileaf collimator (MLC) system. For small-field dosimetry, diodes referred to as “RAZOR detectors,” MOSFET detectors, and Gafchromic EBT3 films were used in this study. For field sizes less than 1×1 cm2, percent depth doses (PDDs) and lateral profiles were measured by diodes, MOSFET detectors, and films, and absolute dosimetry measurements were conducted with MOSFET detectors. For comparison purposes, the same measurements were carried out with a field size of 10×10 cm2. The dose distributions were calculated by the treatment planning system Eclipse. A comparison of the measurements with calculations yielded the percentage differences. With field sizes less than 1×1 cm2, it was shown that most of the percentage difference values were within 5% for 6-MV and 15-MV photon beams with the use of diodes. The measured lateral profiles were well matched with those calculated by Eclipse as the field sizes increased. Except for the depths of 0.5 cm and 20 cm, there was agreement in terms of the absolute dosimetry within 10% when MOSFET detectors were used. There was good agreement between the calculations and measurements conducted using diodes and EBT films. Both diode detectors and EBT3 films were found to be appropriate options for relative measurements of PDDs and for lateral profiles.
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Fig. 1
Calculated and measured percent depth doses (PDDs) at various depths equal to 0.5 cm, 5 cm, 10 cm, 20 cm, and at the depth of the maximum dose (Dmax) for the 6 MV photon beam, and for the field sizes of 10×10 cm2, 1×1 cm2, 0.75×0.75 cm2, 0.50×0.50 cm2, and 0.25×0.25 cm2. The value of Dmax for 6 MV is 1.5 cm. TPS stands for the calculated PDDs using the Eclipse, while Diode and MOSFET stand for measured PDDs using diode and MOSFET detectors, respectively.
Fig. 2
Calculated and measured percent depth doses (PDDs) at various depths of 0.5 cm, 5 cm, 10 cm, 20 cm, and at the depth of the maximum dose (Dmax) for 15 MV photon beams for the field sizes of 10×10 cm2, 1×1 cm2, 0.75×0.75 cm2, 0.50×0.50 cm2, and 0.25×0.25 cm2. The value of Dmax for 15 MV is 3 cm. TPS stands for the calculated PDDs using Eclipse while Diode and MOSFET stand for measured PDDs using diode and MOSFET detector, respectively.
Fig. 3
Calculated and measured lateral profiles at various depths of 0.5 cm, 5 cm, 10 cm, 20 cm, and at the depth of the maximum dose (Dmax) for the 6 MV photon beam for field sizes of 1×1 cm2, 0.75×0.75 cm2, 0.50×0.50 cm2, and 0.25×0.25 cm2. The value of Dmax for 6 MV is 1.5 cm. The calculated and measured lateral profiles are plotted using solid and dashed lines, respectively.
Fig. 4
Calculated and measured lateral profiles at various depths of 0.5 cm, 5 cm, 10 cm, 20 cm, and at a depth of maximum dose (Dmax) for the 6 MV photon beam for the field sizes of 1×1 cm2, 0.75×0.75 cm2, 0.50×0.50 cm2, and 0.25×0.25 cm2. The value of Dmax for 15 MV is 3 cm. The calculated and measured lateral profiles are plotted using solid and dashed lines, respectively.
Table 1.
Percent differences between calculated percent depth doses (PDDs) and measured PDDs for the 6 MV and 15 MV photon beams at various depths equal to 0.5 cm, 5 cm, 10 cm, and 20 cm, and at the depth of the maximum dose (Dmax) for the field sizes of 10×10 cm2, 1×1 cm2, 0.75×0.75 cm2, 0.50×0.50 cm2, and 0.25×0.25 cm2. The Dmax values for the photon beams of 6 MV and 15 MV are respectively equal to 1.5 cm and 3 cm.
| Depth (cm) | Field size | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 10×10 cm2 | 1×1 cm2 | 0.75×0.75 cm2 | 0.50×0.50 cm2 | 0.25×0.25 cm2 | |||||||
| Diode (%)∗ | MOSFET (%)† | Diode (%) | MOSFET (%) | Diode (%) | MOSFET (%) | Diode (%) | MOSFET (%) | Diode (%) | MOSFET (%) | ||
| 6 MV | 0.5 | 0.8 | −1.4 | −4.8 | −4.2 | −5.1 | −2.3 | −6.1 | 2.3 | −9.2 | −7.8 |
| 1.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |
| 5 | 1.4 | 2.9 | −11.9 | −12.5 | −12.4 | −11.8 | −0.9 | 7.5 | 3.0 | −21.6 | |
| 10 | 1.6 | 3.6 | 0.7 | 0.8 | −0.4 | 3.9 | −3.3 | 7.2 | 3.9 | −12.6 | |
| 20 | −0.2 | −4.7 | −0.4 | −9.5 | −2.2 | −4.2 | −6.8 | −2.5 | 2.5 | −9.7 | |
| 15 MV | 0.5 | −8.8 | −13.0 | −11.7 | −12.0 | −13.2 | −9.9 | −16.4 | −12.9 | −20.6 | 15.2 |
| 3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |
| 5 | −5.2 | −6.4 | 0.9 | −0.2 | 1.1 | −1.0 | 0.6 | −0.1 | 2.0 | 6.0 | |
| 10 | −0.1 | −2.9 | 0.8 | 1.1 | 1.1 | 1.7 | −0.6 | 1.8 | 4.2 | 19.4 | |
| 20 | −0.7 | −8.5 | −0.7 | −4.8 | 1.5 | 0.0 | −1.4 | −6.4 | 5.9 | 22.5 | |
Table 2.
Values of absolute doses calculated from Eclipse and measured by MOSFET detectors for the photon beams of 6 MV and 15 MV at various depths equal to 0.5 cm, 5 cm, 10 cm, and 20 cm, and at the depth of the maximum dose (Dmax) for field sizes equal to 10×10 cm2, 1×1 cm2, 0.75×0.75 cm2, 0.50×0.50 cm2, and 0.25×0.25 cm2. Percentage differences were calculated using the measured and calculated values. The Dmax values for the photon beams of 6 MV and 15 MV are respectively equal to 1.5 cm and 3 cm.
| Depth (cm) | Field size | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10×10 cm2 | 1×1 cm2 | 0.75×0.75 cm2 | 0.50×0.50 cm2 | 0.25×0.25 cm2 | ||||||||||||
| Cal.∗ (cGy) | Mea.† (cGy) | Diff.‡ (%) | Cal. (cGy) | Mea. (cGy) | Diff. (%) | Cal. (cGy) | Mea. (cGy) | Diff. (%) | Cal. (cGy) | Mea. (cGy) | Diff. (%) | Cal. (cGy) | Mea. (cGy) | Diff. (%) | ||
| 6 MV | 0.5 | 88.6 | 86.2 | −2.7 | 98.9 | 94.3 | −4.6 | 92.5 | 83.3 | −9.9 | 84.7 | 71.3 | −15.7 | 90.4 | 111.0 | 22.8 |
| 1.5 | 100.0 | 98.7 | −1.3 | 106.7 | 106.3 | −0.4 | 95.4 | 88.0 | −7.8 | 82.6 | 68.0 | −17.6 | 86.4 | 115.0 | 33.1 | |
| 5 | 85.7 | 87.0 | 1.5 | 97.1 | 84.7 | −12.8 | 86.5 | 70.3 | −18.7 | 65.1 | 57.7 | −11.5 | 68.0 | 71.0 | 4.4 | |
| 10 | 66.3 | 67.8 | 2.3 | 61.1 | 61.3 | 0.4 | 54.3 | 52.0 | −4.2 | 46.8 | 41.3 | −11.7 | 49.0 | 57.0 | 16.3 | |
| 20 | 38.6 | 36.3 | −6.0 | 32.6 | 29.4 | −9.8 | 28.8 | 25.5 | −11.7 | 24.7 | 19.8 | −19.7 | 25.8 | 31.0 | 20.2 | |
| 15 MV | 0.5 | 73.5 | 61.6 | −16.2 | 105.95 | 93 | −12.2 | 99.1 | 85.5 | −13.7 | 90.45 | 76 | −16.0 | 75.3 | 86.1 | 14.3 |
| 3 | 99.4 | 95.8 | −3.6 | 132.35 | 132 | −0.3 | 111.7 | 107 | −4.2 | 90.15 | 87 | −3.5 | 71.1 | 70.6 | −0.7 | |
| 5 | 98.9 | 89.2 | −9.8 | 119.5 | 119 | −0.4 | 100.7 | 95.5 | −5.2 | 81.45 | 78.5 | −3.6 | 64.5 | 67.9 | 5.3 | |
| 10 | 76.6 | 71.7 | −6.4 | 93.25 | 94 | 0.8 | 78.55 | 76.5 | −2.6 | 63.65 | 62.5 | −1.8 | 50.6 | 60.0 | 18.6 | |
| 20 | 50.1 | 44.2 | −11.8 | 57.95 | 55 | −5.1 | 48.5 | 46.45 | −4.2 | 90.45 | 76 | −9.6 | 30.9 | 37.6 | 21.7 | |
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